(1) Field of the Invention
This invention generally relates to antennas and more specifically to an antenna that covers a wide frequency band and that can be deployed from an underwater location, such as from a submarine.
(2) Description of the Prior Art
As known, communications between the outside the world and underwater craft, such as a submerged submarine, can be achieved through a floating cable antenna system. With the advent of satellite communications, such antenna systems enable a submarine to remain submerged while communicating with other facilities throughout the world by means of satellite communications in the UHF and other frequency bands.
More specifically, such underwater craft deploy an antenna to the surface to establish communications while the craft remains submerged. After communications are completed, the antenna is reeled back into a storage area. Consequently, the presence of the antenna at the sea surface is minimized to reduce the possibility of detection. Specifically, the antenna as a physical radar contact is detectable only during its presence on the surface.
As an example, U.S. Letters Patent No. 2,067,337 granted in 1933 to Polatzek discloses a flexible tube or hose for deploying an antenna from a submarine. The hose is inflated with air under compression to overcome any loading on an aerial wire in the hose.
U.S. Letters Patent No. 3,788,255 granted in 1974 to Tennyson discloses an expendable submarine receiving antenna. A buoyant capsule has an opening therethrough for release from an ejection chamber in a submarine. The capsule contains a coil of lead-in wire with electrical insulation suitable for use in seawater and having a length that extends between the submerged submarine and the surface. A free end of the wire extends freely through the opening in the capsule for withdrawal and severance of a selected length of the wire for connection at the free end to radio communication equipment aboard the submarine.
U.S. Letters Pat. No. 3,972,047 granted in 1976 to Lombardi for a floating cable antenna system discloses an antenna system in which a submerged submarine tows a buoy by means of an electromechanical cable. A cable reel stores the inflatable buoyant cable and has a pressure accumulator containing a medium under given pressure attached to one end of the buoyant cable. Slip rings provide a communication with the electromechanical cable radio communications.
U.S. Letters Pat. No. 5,132,696 granted in 1992 to Cobb discloses a pneumatic extendable antenna for a water deployable buoy. A whip antenna extends from a shortened configuration to a lengthened configuration. The antenna body comprises a plurality of hollow frusto-conical segments that slidably nest inside each other when the antenna is in its shortened or compact configuration. Filling the container with a pressurizing gas expands the segments relative to each other. A weighted ballast and electronic control circuit attached to one end of the antenna and an air filled stability bag disposed about the antenna near its weighted end orients the antenna in a vertical direction.
U.S. Letters Pat. No. 5,933,117 granted in 1999 to Gehard discloses a flexible ferrite loaded loop antenna assembly. A buoyant loop antenna is deployed along a cable with a core region that comprises a plurality of annular ferrite beads. The ferrite beads are aligned with the concave end of one bead against the convex end of another bead so the cable can flex while the beads maintain contact with each other thereby providing flexibility and resistance to crushing. The core region has a looped wire wrapped helically around it forming the loop antenna. The looped wire elements start and end at the same end of the core region forming a loop. The loop allows reception in an athwart (side to side) direction. The wire loop antenna can be combined with a straight wire antenna to provide reception in a fore and aft direction thereby to provide an omni-directional cable antenna assembly.
Each of these references discloses an antenna that is relatively large and therefore readily detectable at the surface by modern radar systems. With the exception of the Gerhard patent with its complicated ferrite beads that provides some flexibility, the antennas are rigid and not adapted for wrapping on a reel. Many of them require external gas in order to inflate and rise to the surface. Further, each of them tends to be an end fed antenna with the exception of the Gerhard patent that discloses multiple antenna elements to obtain an omni-directional range. The Gerhard patent additionally is directed to VLF/LF transmission bands that incorporate entirely different signal requirements than the typical transmission frequencies in the 200-400 MHz band.
In addition to these antennas, other antennas have been proposed that provide radiation patterns that are more advantageous particularly with respect to satellite communications, but not readily adapted for deployment from underwater craft. For example, U.S. Letters Pat. No. 2,622,196 granted in 1952 to Alford discloses an ultra-high frequency antenna that generates horizontally polarized waves. The antenna comprises a number of small loops shunted across a balanced transmission line arranged so that a large number of loops may be cophasally energized thereby attaining a large concentration of radial power in a plane in which the radiation is distributed in a substantially circular pattern.
U.S. Letters Pat. No. 2,812,562 granted in 1957 to Carter discloses loop antennas for television signals with a loop antenna array of a plurality of loops coupled together by a section of transmission line that has a quarter wavelength, or any odd multiple thereof, at the frequency of operation and having field patterns superimposed in phase quadrature relationship. The loop is preferably a single turn arrangement having a circumference in the order of one or a few wavelengths at the operating frequency and made of a large diameter conductor.
U.S. Letters Pat. No. 3,626,418 granted in 1971 to Barryman discloses a VHF antenna comprising a plurality of closed loop radiating elements that are parallel fed by a tapered pair feed line. Each loop comprises a single turn of conductive material whose dimensions are uniform over the entire loop so each loop is electrically uniform and continuous. The loops are fed in parallel by uniformly tapered feed lines comprising two congruent strips of conductive material that diverge at a small angle. A first loop of said plurality of loops has a circumference equal to one half length at the lowest desired frequency. A second loop has a circumference equal one-half wavelength at the highest desired frequency. The remaining loops are of intermediate size between the first and second loops.
U.S. Letters Pat. No. 3,999,185 granted in 1976 to Polgar, Jr. et al. discloses plural antennas on a common support with feed line isolation. This structure includes a tunable high power MF/HF transmitting antenna having a vertical access and shorting assembly driven along a vertical axis to tune the high power antenna. A plurality of additional antennas are disposed in a vertically stacked relationship above the high power antenna. A tunable ferrite isolator is disposed below a drive shaft and includes a conduit that enables the conduit and the service conductors to pass through the high power antenna with a minimum modification to the performance of the high power antenna.
Of all these antennas, it has been found that the loop antenna, such as disclosed in U.S. Letters Pat. No. 2,622,196, has the potential for providing a desired radiation pattern to a number of applications. However, this structure is a rigid structure that also is not readily adapted for undersea applications. Specifically, it is difficult to store such a rigid structure and to provide any structure that would allow an antenna to rise to the surface.